(1) Field of the Invention
This invention relates to stabilization of organic base substances to light.
(2) Description of the Prior Art
It is widely known that organic base substances, e.g. organic dyes, generally tend to fade or discolor by the action of light. In the field of ink, dyeing of fibers, or color photography, studies have been made to prevent the fading or discoloration of organic dyes or to improve fastness to light.
Hitherto, it is known that organic base substances, e.g. dyestuffs or dyes, have a tendency toward fading or discoloration. A number of reports have been submitted with respect to methods of reducing the fading or discoloration or methods of improving fastness to light. For instance, U.S. Pat. No. 3,432,300 describes an improvement in fastness to visible and UV light by mixing organic compounds, such as indophenol, indoaniline, azo and azomethine dyes, with phenolic compounds having fused heterocyclic rings.
In the field of silver halide photographic materials, azomethine dyes or indoaniline dyes are formed by reaction between oxidants of aromatic primary amine photographic developers and couplers as is particularly set forth in Chapter 17 of "The Theory of the Photographic Process, by C. E. Mees and T. H. James (Macmillan Pub. 1967)". A number of methods of improving light stability of images formed from these dyes or color images are known. For instance, there are known methods using hydroquinone derivatives as described in U.S. Pat. Nos. 2,360,290, 2,418,613, 2,675,314, 2,701,197, 2,704,713, 2,728,659, 2,732,300, 2,735,765, 2,710,801 and 2,816,028 and British Pat. No. 1,363,921, gallic acid derivatives as described in U.S. Pat. Nos. 3,457,079 and 3,069,262 and Japanese Patent Publication No. 13,496/1968, p-alkoxyphenols as described in U.S. Pat. Nos. 2,735,765 and 3,698,909, and derivatives such as chroman and coumaran as described in U.S. Pat. Nos. 3,432,300, 3,573,050, 3,574,627, 3,764,337, 3,574,626, 3,698,909 and 4,015,990. However, these compounds serve, more or less, as an inhibitor for fading or discoloration of color images but are not satisfactory.
British Pat. No. 1,451,000 describes a method of improving light stability of an organic base compound by the use of azomethine extinction compounds whose absorption maximum is larger than an absorption maximum of the organic base compound. However, this method is disadvantageous in that because the azomethine extinction compound is deeply colored, it greatly influences the hue of the base compound.
Use of metal complex salts for preventing optical deterioration of polymers is described in J. Polym. Sci., Polym. Chem. Ed., by J. P. Guillory and R. S. Becker, 12, 993 (1974) and J. Polym. Sci., Polym. Lett. Ed., by R. P. R. Ranaweera and G. Scott, 13, 71 (L975). A method for stabilizing dyes with metal complex salts is described in Japanese Patent Application (O.P.I.) No. 87,649/1975 and Research Disclosure 15162 (1976). However, these complexes do not a great fading-inhibiting effect and are not high with respect to solubility in organic solvents. Thus, it is not possible to add the complexes in amounts sufficient to cause the fading-inhibiting effect to be satisfactorily shown. Moreover, these complexes are deeply colored, so that if added in large amounts, they adversely influence the hue and purity of organic base substances, particularly dyes.